Research And Application Of Optical Anisotropy And Nonlinear Based On Subwavelength Metal Structure

With the development of industry and society,high requirements are imposed on the integration of optical devices.Surface Plasmon Polaritons(SPP),as the only method that can regulate and process optical signals in the sub-wavelength range,has been widely studied.In these works,there are a lot of studies on the nonlinear effects of SPP.However,it can be found that these works mainly focused on the nonlinear process from SPP to light of free space propagation.And it lacks the nonlinear process from SPP to SPP,which is actually not conducive to future optical integration design.In order to solve this problem,we have studied this nonlinear process.Before this work,because most nonlinear materials are often anisotropic,we have also studied the anisotropic properties of SPP,which is rarely studied.In this thesis,we mainly studied the anisotropic and nonlinear characteristics of SPP.In the work of anisotropy,we discovered new phenomena caused by anisotropic materials and designed devices based on it.In the study of non-linearity,we mainly studied the second harmonic generation of SPP and the wave vector matching of it.The main results are as follows:1.A metal-insulator-metal plasmonic structure that contains a circular cavity with anisotropic material(AM)is designed and numerically simulated.Attributed to filling the cavity with AM,the standing wave patterns in the cavity rotate clockwise as the wavelength increases,resulting in a new valley on the transmission spectrum,which will not appear in the isotropic-material case.In order to understand the underlying physical mechanism of the phenomena,the influences of the parameters of AM,such as optical axis angle and refractive indexes,on transmission spectrum were investigated.All results can be explained well by the index ellipsoid method and the coupled mode theory.Finally,we designed a demultiplexers based on above results with 8 nm resolution.This work shows the unique role of AM in the plasmonics nanostructure and these phenomena may have potential applications in the nanoscale integrated photonic circuits.2.We theoretically studied a planar waveguide of SPP based on an anisotropic material(AM).According to theoretical results,owing to the anisotropy of materials,the field distribution tilts in the AM layer of the waveguide,which is barely observed in isotropic material.The tilt of the field is demonstrated by simulation and causes a phase difference between the fields at different waveguide boundaries.The dependence of the inclination angle on the optical axis angle of AM is also obtained.Based on a tilted field,a symmetrical plasmonic structure with AM is designed,which can output two SPPs with a phase difference of ?.Because of this characteristic,the structure can operate as an XOR logic gate with an excellent extinction ratio.Simultaneously,the structure can also be made into an OR logic gate on another operating wavelength without any structural changes,which means that the structure can achieve parallel computing.Through the electro-optic effect of AM,the structure can also function as a light switch.The phenomena investigated in the paper may be useful in the nanoscale integrated photonic circuits,and the proposed structure shows the potential of AM to be used to fabricate logic devices.3.We theoretically studied the second harmonics generation of SPP to SPP.First,we deduced from the Maxwell equations to obtain the second harmonics generation equation of SPP.After that,we tried to use anisotropy to achieve wave vector matching of that,however,it is failed.We get inspiration from the coupled mode theory and consider the second harmonics generation as a process of mode coupled.Then,the wave vector matching is successfully realized by using the grating structure,according to the theory.What's more,those even-order gratings cannot achieve wave vector matching in the simulation are also well explained by the above theory.Finally,we designed an experimental scheme to verify that the gratings achieve the second harmonics generation of SPP.This work reveals the second harmonics generation process of SPP,and has promoted the understanding of the nonlinearity of SPP.